Ah. Rule 12.
Looks as if I won't be visiting WA.Quote:
12. Minimum speeds on freeways
In a freeway speed zone, a person shall not drive a vehicle at a speed that is more than 20 km/h below the speed limit unless —
(a) traffic congestion prevents the person from driving the vehicle at a speed that is within 21 km/h of the speed limit; or
(b) for any other reason, it is unsafe or imprudent for the person to drive the vehicle at a speed that is within 21 km/h of the speed limit.
Modified penalty: 1 PU
Oh, it's a local rule. Not in the national rules. Maybe it should be. That'd get the trucks off our roads for sure. I often sit behind trucks maxing out at 60km/h in a 110km/h zone up hills.

